Low shrink resin

High gloss surfaces can only be produced from highly polished molds. Also, careful design of ribs and bosses, plus the gating location in the mold, will help to minimize localized surface depressions and flow lines around inserts and pins in the mold. When high-gloss surfaces are required, low shrink resin systems should be used. Num-... 

Choose low-shrinking resins, e.g., epoxies rather than unsaturated polyesters. 

Papadogiannis, D. et al. (2009) Setting characteristics and cavity adaptation of low-shrinking resin composites. Dent Mater., 25 (12), 1509-1516. 

The tendency of thick sections of DMC structural parts to crack has been overcome by using low-profile polyester resins (or low-shrink resins). These are prepared by making a blend of a thermoplastic (e.g., acrylic) polymer-styrene system with a polyester-styrene system. Moldings of this blend cured at elevated temperatures exhibit negligible shrinkage and minimal warpage and have very smooth surface, to which paint may be applied with very little pretreatment. 

A wide spectrum of properties maybe obtained by varying the ratios of thermoplastics, polyester, and styrene in the blend. Among the thermoplastics quoted in the literature for such blending are poly (methyl methacrylate), polystyrene, PVC, and polyethylene. High-gloss DMCs using low-shrink resins have found uses in kitchen appliances such as toaster end plates, steam iron bases, and casings for electric heaters. 

With either EBM or IBM, the requirement for a thermally controlled parison at the lowest heat increases the demand on internal pressure/vol-ume to ensure adequate movement or expansion of the parison in the transverse direction. It is possible that vacuum-aided stretch blowing can provide faster expansion rates of the parison and improve performance at the higher stretch-blow ratios. With PVC, PS, and other low shrink alloyed resins, the vacuum assist may need little or no pressure beyond one atmosphere. The function of vacuum (—14.7 psi) has the basic effect of — ( —14.7 psi)... 

A high performance polyester containing less than 35% styrene monomer designed for marine laminates and as well as offering excellent surface quality, low shrink, impact and blister resistance meeting the requirements of the Southern California Air Quality Management District Rule 1162 for volatile organic compound resins. 

An unaccelerated resin specifically designed for the manufacture of low shrink, SMC/BMC moulding compounds. 

A specially blended resin series for RTM and low press moulding where low-shrink, non-warping and/or a Class A surface is required, c. 01 = 100-130 and 04 = 90-150 e. 6-9/25... 

A preaccelerated, low shrink, low exotherm, resilient resin designed for cultured mait)le casting applications, being particularly recommended for hot weather application, tubs, shower pans, complicated parts or wherever a more forgiving resin is desirable. Offers resistance to warping and cracking. 

A preaccelerated, low shrink, low exotherm, resilient resin designed for cultured marble casting applications... 

A low shrink, low profile resin containing vinyl ester for SMC and BMC applications, with high heat resistance and high tensile elongation. Can be employed as a low profile additive - see section H8. 

A medium to highly reactive isophthalic base resin suitable for low profile/low shrink SMC/BMC manufacture. Thickenable. 

A highly reactive, high viscosity orthophthalic resin which in combination with low shrink and low profile additives, is suitable for SMC manufacture and then car body, furniture and electrical mouldings, b. 72% c. 3900-4910... 

A white, free flowing paste-like solution or dispersion of thermoplastic polymers and fillers for low-shrink application in highly reactive fire retardant, SMC/BMC and puitrusion resin systems. 

Because of their lesser ability to control shrinkage, the non-polar polymers such as polystyrene and polyethylene are often classified as low shrink rather than low profile additives. Usually, low profile additives are supplied as 30-40% polymer solutions in styrene monomer. Polyester resin manufacturers also package the low profile additives dissolved in their resins. These are referred to as one pack systems. As the industry has expanded, other thermoplastics have been identified which have shrinkage control properties. These are also now used commercially in a variety of applications. Examples of these other polyers are saturated polyesters, polyurethanes, stryene-butadiene copolymers and polycapro-lactones. Polyfvinyl acetate) based materials are probably still the most used low profile additives, being useful with the broadest range of unsaturated polyester resin structures. Relative proportions of the organics used in most formulations are 30-50% polyester alkyd, 10-20% thermoplastic and 40-50% styrene. 

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